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Functional Groups in Organic Chemistry
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0:07
So what is a Functional Group? In Organic Chemistry you'll see a lot of molecules that are made up of carbons and hydrogens. You can get many complex structures and many isomers from just carbons and hydrogens. Before molecule to be reactive it tends to have other atoms with different electronegativities, different electrons, concentrations, pi bonds. Those specific groups, those are your functional groups. Now before we go into Functional Groups, I want to talk about one type of group that
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you'll see that's not functional group at all and that's the R group. As we look into your textbook you'll see molecules that has carbons, oxygens, nitrogens, and an R group. But an R group does not represent a specific collection of atoms, instead the R group tells you what you have on the rest of the molecule. For example, if I'm looking at this structure here, but then I have a complex group of a C double bound O, single bound O, single bound
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to another C with three hydrogens and I specifically want to focus on this portion of the molecule. I don't want to look at the carbon chain, it's not my priority for this discussion. So instead of reading this entire molecule and the group that I boxed off, I'll turn the entire purple portion in R for the rest of the molecule, and then simply focus on the ester here which is a CO2CH3. R is the rest of the molecule that I don't want to
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focus on right now but I still acknowledge that it's there. When talking about functional groups, you'll typically see R-functional group to show that it can come up at any type of molecule. Another thing to discuss before we go into Functional Groups are the type of carbon chains that you're going to see specifically the Alkane, Alkene, and Alkyne. Notice the ending Alkane is "ane", Alkene is "ene",Alkyne is "yne". And this tells you the number of pi
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bonds specifically carbon to carbon pi bonds that you're going to see. An Alkane has no pi bonds between carbon atoms, that means every atom is single bound to another carbon. You'll see this drawn out in line structure as a zigzag where every carbon is sp3 hybridized with an ideal bond angle of 109.5 degrees. An Alkene is a molecule that has at least one double bond between carbon atoms.You'll see that as carbon double bound to carbon
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where the first bond is the sigma and that's with your hybridized orbitals and the second is a pi bond sitting in the p-orbitals. In line structure, it'll look the same as your alkane except that you'll see a second line representing the pi bond. You can have more than one double bond on a molecule as long as they're different carbon atoms that have the pi bond so that each is still considered a double bond. The carbons holding the double bond are sp2 hybridized with a bond angle of 120 degrees.
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And finally we have the Alkyne which is a triple bond between two carbon atoms. Notice here we have two double bond because each individually has a double bond, but with an Alkyne you'll see a three lines between two carbon atoms. The first is at sigma and that's on your sp hybridized carbon, the second and third are your pi bonds sitting in p-orbitals, one in the p y and one in the p z. Many professors will try to represent a triple bond the same
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way as a double and a single in terms of a zigzag, but this is incorrect and I don't like it. And that's because a triple bond is sp hybridized with a bond angle of 180 degrees and so the correct way to represent it is something like this. You wanna have a linear line where the triple bonds sits between the two carbon atoms, that would be this two right here, but the two carbon atoms or other atoms on either direction of the
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triple bond are also in a straight line because of that 180-degree bond angle. Now that you understand it, let's memorize it. I have to memorize as 1, 2, 3, ane, ene, yne. Ane is one, single bond, ene is two, double bond, yne is three, triple bond. The first and simplest functional group we'll look at is the Alkyl Halide or the Haloalkene. Recall from general chemistry that group 7 on the periodic table are your halogens or
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your halides, that's where we get the alkyl halide and these are Fluorine, Chlorine, Bromine, and Iodine, in that order going down the group. If you have a carbon chain with any halogen attached to, that is considered an Alkyl Halide or a haloalkane and you just insert the name of the halogen to be more specific. So for example, if I put a Chlorine on the primary carbon here, I will get a primary Alkyl Chloride or Chloroalkane or simply a primary alkyl
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halide. If I place Iodine on the secondary carbon, I get a secondary Alkyl Halide. If you're comfortable identifying your Primary, Secondary, and Tertiary carbons, make sure you study my Pencil Trick Tutorial linked on the description below. And if I place a Fluorine on a tertiary carbon I get a tertiary halogen or a tertiary alkyl halide. These are very important to understand and recognize because they will play a big role in the reactions
5:50
moving forward especially substitution and elimination reactions. The next functional groups I want to look up are the Amines which have n in the word where n stands for the Nitrogen atom. An Amine is a molecule that has Nitrogen bound to Carbon and this could be bound to a 1, 2 ,3 or 4 carbons to give you a different type of Amine. To show you the different types of Amines, we'll use R to represent the rest of the molecule.
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If I have R bound to an NH2, remember a Nitrogen can have three bonds. This is considered a primary amine because it's bound to one R-group. If I have R bound to Nitrogen which is bound to a second R, which we'll show as R-prime, this is considered a secondary amine because Nitrogen is bound to two R-groups. If I have a Nitrogen bound to three R-groups, that's R, R-prime, and R double prime. That's a tertiary amine and these are the common ones we're
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going to see. But every now and then you'll see a Nitrogen bound to four R-groups that'll be bound to R, R prime, R double prime, and R triple prime. If you'll do a quick formal charge, you will recognize that the Quaternary Amine has a positive charge because Nitrogen prefers to have three bonds and one lone pair. But if and when it comes out recognize that yes a Quaternary Amine does exist. And the key to recognizing the Amine functional group,
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Amine spelled with an n has the key atom Nitrogen. Many of the remaining functional groups will have Oxygen in them and the key is to recognize the difference between how the Oxygen is attached to the parent chain. The alcohol has COH in a name where C can be a part of your R-group. So if you have your R-group and attached to that you have a C, an O, and an H, that's an Alcohol where the alcohol is the OH or Hydroxyl group. Hydroxy comes from the word Hydrogen and Oxygen. So if you see a carbon
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chain with an OH on the primary carbon, that's a primary alcohol. If the OH was on the tertiary carbon, that would be a tertiary alcohol. A similar functional group is the Thiol which you'll notice sounds like Alcohol, it ends in OL which is how you identify an alcohol, but the Thi portion of the molecule represents the sulfur atom. So if we take a molecule and draw an alcohol, but now we erase the Oxygen and replace it with a sulfur, this is a sulfur alcohol or simply a Thiol. Recall
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that sulfur sits on the Oxygen on the periodic table so they have very similar binding ability. The next group I want to look at is the Ether and this is one of the first confusing functional group. An ether is represented by R,O,R. We have an Oxygen sitting between two carbon groups. You can have a symmetrical ether, for example if I have CH3-O-CH3, this is dimethyl ether because I have two methyls surrounding that Oxygen. You can also have an asymmetrical
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ether, for example, if I have a CH3 bound to an O, the second R-group is a CH2CH3 or an ethyl group, this is ethyl methyl ether where the tro R-groups are different. And in this case we have to write it as R-O-R prime. A good trick to remember the Ether is to think of the word Either, it looks like we have R-O-R, we have either R or something else. Ether or Ether has OR in the word. Do not confuse the Ether with an Ester which
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we'll look at shortly. Ethers can exist as a linear chain like we see here, or you can see a cyclic ether. For example if I'll show you a five numbered ring where we have four carbon atoms and one Oxygen, this is still an ether, it's a cyclic ether, it's one that you'll have to know later in your Organic Chemistry reactions. This is tetrahydrofuran or THF, which comes up a lot on reactions. You don't have to memorize the name of cyclic ether except for this one, the Epoxide. Epoxides
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are very reactive and will come up a lot in Organic Chemistry so I want you to recognize it. Epoxide is a three membered ether, we have a three atom ring, two carbons and one Oxygen. You can have carbons or Hydrogen coming off of it but the key is the small triangle made up of two carbons and one Oxygen giving you an epoxide. The next set of functional groups we'll look at will have the carbonyl in common. Where carbonyl is C double bound
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O. This will be very important later on because the carbonyl has resonance and that means you get a partial positive on a carbon and a partial negative on Oxygen. But for now we'll focus just on the structure. And since there's a pi bond between them, where the carbon and Oxygen are sp2 hybridized with a bond angle of 120 degrees. When you have the carbonyl in the middle of the chain, meaning the carbonyl has R-groups
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on either side, you get a ketone. The way I remember this is Ketone ends in "one". A ketone does not want to be alone, one it doesn't wanna be alone, and therefore it's surrounded by R-groups on either side. If I wrote this out showing the atoms we would see CH3 bound to the carbonyl, bound to the CH3 because it's in the middle, it doesn't want to be alone. Just like the Ether, the Ketone can be symmetrical, in this case we have two methyl
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groups, or it can be asymmetrical if I replace the methyl group on the right with an ethyl group. This is also a ketone. If you see this written out, you'll see this as R carbonyl and R or R prime depending on if the second R-group is the same or different. Or of the pi bond are not being shown, this is R C O R. Don't mix this up with an Ether which was just R-O-R because we have the carbon there, it's not an Oxygen in the chain, instead it's a carbon in the chain double bound to an Oxygen atom.
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Aldehydes are very similar to ketones so don't confused the two. The aldehyde also has a functional group on a carbon chain but in the aldehyde's case it's not in the middle of the molecule like the ketone that doesn't want to be alone. Instead, the carbonyl is at the end of the molecule so that the last atom here is the Hydrogen. The aldehyde has an H in the word to remind you that there is a Hydrogen in the end rather than another
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carbon or another R-group. If we write this our we have CH3CH3CH2 for the propyl group, then we'll have C double bound O for the carbonyl and H for the Aldehyde. If you want to write this out in simple terms,it'll be R carbonyl H instead of R carbonyl, R prime like the ketone or we can write it out even simpler, RCHO. This is another source of confusion for students, I wanna make sure you understand. RCHO has the carbon then the hydrogen then
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the Oxygen telling you that it's carbon, then bound to Hydrogen, the Hydrogen sits on the carbon and the Oxygen has to come back and be written on the carbon. Don't confuse this with the alcohol which we showed as RCOH, if it's O then H it's an alcohol because you have carbon followed by Hydroxyl OH. But an aldehyde is not Hydroxy, it's HO giving you a completely different functional group and a completely different molecule.
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The next functional group I want to look at is a carboxylic acid and this is another source of confusion for students so make sure you understand. The carboxylic acid has a carbon chain with a carbonyl at the end. C double bound to O and then attached to that, we have an OH. Students will look at this and think "oh! I have a carbonyl and then alcohol", but that is not the case. Whenever you see a carbonyl directly attached to an OH, that
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is not an alcohol attached to an aldehyde, that is a brand new functional group, the carboxylic acid. If we'll write this out we have CH3CH2 for the upper portion, then the carbonyl and OH. If we want to write this out even more simply, we can have R to represent the ethyl group or the rest of the molecule , COOH. You'll also see it as RCO2H. We're showing that there are two Oxygens on this functional group. One Oxygen sitting on the
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carbon in a double bond, the second Oxygen sitting on the side as an OH. As you'll see late in Organic Chemistry 2, carboxylic acids can be reactive so that the OH is swapped for another group and those are your Carboxylic Acid derivatives giving you a whole new set of functional groups. The first one we'll look at is what happens when we take that OH on the carboxylic acid and replace it with an OR. This molecule is called an Ester. For example, if we swap this
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R-group for a CH3, we'll have CH3, CH2, C double bound O, single bound O, single bound CH3, for a methyl ester, because it's a methyl sitting on the longer parent chain. If you wanna write this out the short way, the ester is RCO2R prime. Just like a carboxylic acid RCO2 or RCOO, but instead of a Hydrogen at the end, we have an R-group at the end. Esters are often confused with Ethers so I want to make sure you'd see them together and understand
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the difference. If we have an Ester that's R CO2 R-prime, and Ether is just R-O-R prime. Remember for Ethers we said it's either OR, that's it. It's R and O R, nothing else. Either R or the OR. An Ester has an S. Think of that S as standing for your second R-group. Because Ester looks like a Carboxylic acid but it has a second R-group and then the example we saw above that's second R-group as a methyl. One more time we have our carboxylic acid
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but this time, I'm going to replace that OH with the Nitrogen. So for example if I replace it with an NH2 I get a new functional group and this one is the Amide. Amide sounds very much Amine, but remember the Amine, we set "n" for Nitrogen. When Nitrogen was the primary focus on the functional group because we have just Nitrogen and carbon, R-groups, nothing else. The Amide looks like a carboxylic acid and sounds like Amine. We'll it looks like
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a carboxylic acid because it's a carboxylic acid derivative and it sounds like Amine because we have a Nitrogen in there and the 'd" is to remind you that in addition to the Amine portion, we also have a double bond carbon Oxygen. "D" for double bond carbon to Oxygen on a molecule that sounds like Amine. Just like Amines, when it comes to amides, it doesn't have to be just an NH2. We can have NH2, a simple Amide, or we can add some R-groups in there.
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For example I can put a CH3 with one Hydrogen or 2 CH3s or any R-group. I just chose methyl with no Hydrogen, because Nitrogen remember likes 3 bonds and 1 lone pair. These are different types of molecules that you have to recognize as an Amine. It sounds like an Amine, it looks like an Amine, but the D reminds you that there's also a double bond carbon to Oxygen in that same functional group. There's another Nitrogen containing another functional group
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that has R and then C triple bound N. This right here is called a Nitrile, it's also referred to as a cyano group because CN- is cyanide comes from cyanic acid. This will come up in your Organic Chemistry reactions so make sure you do recognize it, the Nitrile has a C triple bound to N on the carbon chain. The last group we'll look at is not really a functional group but it comes up so often and students mixed it up so often so I wanna make sure you're clear on the difference.
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Phenol vs. Phenyl. A Phenyl and a Phenol, they kinda sound similar but a Phenol ends in OL which tells you that it's an alcohol, right alcohol also ends in OL and Phenyl ends in "yl". In naming Organic compounds where you have an R-group as a substituent, it ends in yl. For example a CH3 is a methyl, a CH3CH2 is an ethyl, yl. The beginning of the word the "phen" portion should hint benzene ring and it's simply a question of what the benzene
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ring looks like. The Phenol is a benzene ring alcohol. That means we have a benzene ring, a 6 carbon chain with alternating pi bonds and an OH attached to it. That's it! it's not attached to a bigger chain, it doesn't have anything else coming off it. Phenol Alcohol, but when you have just Phenyl that is the benzene ring as a substituent on a larger chain. So we'll show instead of an alcohol, an R-group attached to it. If you have a giant
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molecule with a benzene substituent,that substituent is a Phenyl, yl substituent. Not to be confused with the Phenol which is a benzene ring alcohol. I hope this video helps you not only understand but to look for functional groups but also gives you couple of tricks to help you memorize them. First thing I want you to do, give this video a thumbs up and leave a comment below letting me know if it helped you and which
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mnemonic you like best then make sure you visit my website leah4sci.com/Naming so that you can download my FREE full color functional group cheat sheet as well as try the Practice Quiz. And then start working through the naming series showing you how to tackle each functional group including IUPAC and Common Names. The link again is leah4sci.com/Naming.
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